Electronic devices generate heat during operation. Thermal management refers to the ability to keep temperature-sensitive elements in an electronic device within a prescribed operating temperature.
Historically, electronic devices have been cooled by natural convection. The cases or packaging of the devices included strategically located openings (e.g., slots) that allowed warm air to escape and cooler air to be drawn in.
The advent of high performance electronic devices, such as processors, now requires more innovative thermal management. Each increase in processing speed and power generally carries a “cost” of increased heat generation such that natural convection is no longer sufficient to provide proper thermal management.
One common method of cooling electronic devices includes thermally coupling a heat sink to the electronic device. A typical heat sink includes protrusions, such as fins or pins, which project from a body of the heat sink. The protrusions give the heat sink a larger surface area such that the heat sink dissipates a greater amount of thermal energy from the electronic device into the surrounding environment. Heat sinks are fabricated from materials with high thermal conductivity in order to efficiently transfer thermal energy from the electronic device.
Heat sinks are sometimes positioned against an electronic device and then attached to a system motherboard during a wave-soldering process that is typically part of motherboard manufacturing. As an example, heat sinks are commonly thermally coupled to some low-power electronic devices that are mounted on a motherboard in the vicinity of a CPU on the motherboard. The heat sinks are mounted to the motherboard by wave-soldering pins that extend through openings in the heat sink and throughholes in the motherboard.
One drawback with wave soldering pins to the motherboard is that, when the solder joints between the pins and the motherboard are subjected to temperature cycling stresses representative of accelerated use conditions, the solder joints become cracked, compromising the structural and thermal benefit of the heat sink. Temperature cycling stresses are generated on the solder joints because of the differences in the coefficients of thermal expansion between the materials that are used to manufacture heat sinks and motherboards.
As CPU power densities continue to increase, so too does the structural and thermal challenge related to designing platforms for the system manufacturing industry. High power CPU's are typically thermally coupled to a heat sink with a very large mass (450 grams or more). The heat sink that cools the CPU usually requires a large mass in order to meet the cooling requirements of the CPU. The large mass of the CPU heat sink generates unwanted shock and vibration stresses on any lower power electronic devices (e.g., graphics memory controller hub) that are mounted on the motherboard in the vicinity of the CPU and associated CPU heat sink. The shock and vibration stresses can be especially problematic when the motherboard is transported from one location to another.
One example relates to when a motherboard is mounted within a chassis that is shipped to an end user. The ball grid array (BGA) solder joints, which are often used to mount low-power electronic devices on the motherboard in the vicinity of the CPU, are particularly vulnerable to the shock and vibration forces generated by the high-mass CPU heat sink during shipping. Therefore, the heat sinks that are coupled to the low-power electronic devices on the motherboard are used to provide structural support to the BGA solder joints that connect the low-power electronic devices to the motherboard, and to provide thermal cooling to the low-power electronic devices.
There is a need for a heat sink assembly and method that securely couple a heat sink to a motherboard and to an electronic device mounted on the motherboard. The heat sink assemblies and methods should be able to partially absorb the shock, vibration and temperature cycling stresses that are typically generated on the solder joints within such assemblies.